To reduce man-hours and the cost of construction at the time of constructing a vertical light duct on the spot and to enables to secure a parallel light duct surface opposing ends other.

As shown in (a), the light duct panel 2, which is beforehand cut in predetermined length, is rolled up in a shape of a coil so that a reflective face may become inside, and the one side end of the light duct panel is attached to an upper end of a wall surface 1 by an attachment component 3. And the light duct panel rolled in the shape of the coil is taken down slowly while rewinding, by hanging it with a string or the like. If the another side end of the optical duct panel 2 reaches the lower end of an wall surface, as shown in (b), the other side end of the light duct panel 2 is fixed with the attachment component 4 of the a wall surface. A mechanism, which gives downward tension to the light duct panel 2, is prepared in the attachment component 4, and by this, the curvature and slack of the optical duct panel are canceled.